Visual speech form influences the speed of auditory speech processing.

An important property of visual speech (movements of the lips and mouth) is that it generally begins before auditory speech. Research using brain-based paradigms has demonstrated that seeing visual speech speeds up the activation of the listener's auditory cortex but it is not clear whether these observed neural processes link to behaviour. It was hypothesized that the very early portion of visual speech (occurring before auditory speech) will allow listeners to predict the following auditory event and so facilitate the speed of speech perception. This was tested in the current behavioural experiments. Further, we tested whether the salience of the visual speech played a role in this speech facilitation effect (Experiment 1). We also determined the relative contributions that visual form (what) and temporal (when) cues made (Experiment 2). The results showed that visual speech cues facilitated response times and that this was based on form rather than temporal cues.